It is known to utilize a tensioning device to effectively operate a variety of rotating accessories operatively connected with and driven by an engine. In order to maintain reliable and efficient operation of the accessories, the tension of the belt should be maintained at a level sufficient to prevent slipping of the belt over various pulleys upon which the belt is trained.
Consequences of the slippage of the belt can be undesirable. Particularly, slippage can be disastrous in case of the chains used to drive an engine's valve gear. The slipping of accessory drive belts used for the purpose of providing power to such engine accessories as a power steering pump, air conditioning compressor and many others, while not producing catastrophic results, still leads to its inefficient operation and is accompanied by undesirable squealing and chirping noises. Accordingly, the need for belt tensioning under such circumstances has been recognized for many years.
Typical in many respects of the known prior art, a belt tensioner shown in FIG. 1 includes a stationary bracket 8' and a pivotal arm 5' functioning as a pulley support. The illustrated device is negatively affected by a few drawbacks. First of all, because the tensioning device is secured to the engine, the attaching structure lacks rigidity and as a result may have vibration characteristics which are far from being ideal. This, in turn, leads to unsatisfactory rigidity of the structure which negatively affect the tensioning of the belt.
The device shown in FIG. 1 is particularly unsatisfactory because it has a very limited supporting surface between the arm and the bracket. As known in the art, facing surfaces of the stationary and displaceable elements of the tensioner are abutted by respective bearing surfaces. Thus, as can be seen from FIG. 1, a central axial bearing 12' contacting the arm 5' and the bracket 8' is practically a single wear surface which provides stiffness to the whole structure. As demonstrated by practical application of such tensioners, this structure is inadequate and results in a short life of the tensioner. It needs frequent maintenance and, therefore, is neither cost efficient nor practically durable.